This invention relates generally to a technique to improve the manufacture of metal castings, particularly in a production line environment. The invention relates, more particularly, to a technique for preventing molten iron which is being poured into a first cavity from being splashed, overflowed, or otherwise inadvertently introduced into an adjacent second cavity. Most particularly, this invention relates to improvements in production line casting techniques which use continuously produced molds of the "door and ram" type, such as those involved with the well known "Disamatic" machine.
Production line casting of molten metal typically involves large scale, complex operation. A batch of molten metal weighing several thousand pounds at temperatures in excess of 2000.degree. F. must be formed into individual castings in the relatively short time interval during which the temperature of the metal remains within a certain temperature window, i.e., a temperature range with upper and lower limits whose numbers depend upon the metal and component being cast.
The molten iron is typically held in a large ladle. Castings are made by pouring molten metal from the ladle into a cavity. The passage leading from the surface of the mold to the cavity is referred to as the downsprue. The cavity and downsprue are formed by various techniques according to the selected method of mold manufacture.
One technique for mold manufacture, not involved with this invention, creates molds which are sometimes described as "cope and drag" molds. For purposes of this invention, these mold types involve a top mold half and a bottom mold half which join together to define a single, distinct mold having a distinct cavity. Such a mold is physically separate and distinct from other similar molds in the casting operation and, thus, the problem of splashing or overflow of molten metal from one mold to another is relatively small.
Another technique for mold manufacture, which is associated with this invention, creates a mold having two embossed surfaces, i.e., a front surface and a rear surface. The front embossed surface, referred to as the "door half," embodies one-half of the cavity and downsprue. The rear embossed surface, referred to as the "ram half," embodies the second half of the cavity and downsprue. In operation, the door half of a first mold abuts the ram half of a second mold to form a complete cavity and downsprue. Molds formed in this manner do not function as separate and distinct molds, but rather do function and advance in series sequence, because any given mold can only create a cavity and downsprue in cooperation with an adjacent mold. Molds of this type are made by the well known "Disamatic" machine. Other similar examples of such mold making techniques are also commercially available and well known.
When molten metal is poured into a first cavity during a production casting operation of the series sequence type, the molten metal may inadvertently enter another cavity which happens to be adjacent the first cavity. For the purpose of this application, the term "first cavity" will refer to that cavity in the casting operation which is the intended recipient of molten metal being poured at any specific time. Similarly, for the purpose of this application, the term "second cavity" will refer to a cavity which happens to be adjacent to or, more generally, in the physical proximity of the first cavity.
The inadvertent introduction of molten metal into the second cavity can occur in various ways. Molten metal may overflow from the first cavity into the second cavity. Alternatively, molten metal may splatter when it is poured into the first cavity, and droplets of the molten metal may splash into the second cavity.
Regardless of how it occurs, the introduction of molten metal into the second cavity creates serious quality control problems for the casting manufacture. The molten metal cools rapidly in the second cavity, forming nodules of solidified metal referred to as "cold shots". The metallurgic properties of cold shots will usually be unacceptable and outside the range of acceptable metallurgic properties for which the casting was designed, because the cooling rate of the molten metal in the area of the cold shots will have been substantially altered from the intended rate of cooling. Moreover, if molten metal is subsequently poured into the second cavity, i.e., when the second cavity is moved into the pouring position, the newly poured metal may not properly bond with the cold shots. These and other related situations can give rise to a variety of serious deficiencies in the casting.
Casting companies have developed various ad hoc approaches to this problem. However, no known effective solution to this problem has developed heretofore. Moreover, many of the prior attempts by the trade to solve the problem have been treated as trade secrets by casting manufacturers and have not been disclosed to the public. As a result, relatively little information is believed to be publicly available on solutions for this problem.